In the list of geodetic works, you can sometimes find such a service as determining the composition of the soil. This procedure is performed in order to obtain information about the content of particles in the soil in a particular area. In construction work, the definition of such a composition is required infrequently, but in agriculture and geological exploration activities can not do without it. In this case, the particle size distribution can be determined by different methods. The choice of one of them depends on many factors and conditions.
General information on particle size distribution
Granulometric composition refers to the presence of mechanical elements in the soil. Moreover, in this case, the soil can be considered as a general designation of soil, which can also be artificial. As for particles, they can have different characteristics and origin. Also, different types of compositions are found in concentration. For example, the granulometric composition of sand will be more or less uniform, even in terms of the content of particles of a certain fraction. Experts note that the minimum size of elements that are able to identify the practiced techniques of this analysis is only 0.001 mm.
In accordance with GOST, six types of fractions are distinguished - these are the same sand particles, block, gravel, clay, etc. Each fraction has not only its own range of sizes, but also biological origin. At the same time, one should not think that the granulometric composition is characterized only by the content of small particles. GOST under the number 12536-79 also notes that the maximum size of the fraction, which is considered as an integral part of the soil, reaches 200 mm. These are mainly boulder elements, which can also have large sizes. The smallest fraction is clay, although sand particles can compete with it in this indicator.
Granulometric classification
In addition to fractional gradation of soils, there are other classification principles. One of them provides for separation based on indicators of the content of clay particles. In this case, the nature of soil formation is also taken into account and the dominant fraction is revealed. An alternative classification is to determine the type of composition through the presence of elements of sand, dust and the same clay. That is, in some way, such a particle size distribution will be determined by a combined principle with a comprehensive presentation of information about the elements included in it. It is important to note that due to the similarity between the two approaches to the classification of compounds, it is rather difficult to distinguish between them in practice.
Direct methods for determining the composition
There are two fundamentally different groups of methods for determining the mechanical composition of the soil. One of them is indirect and designed to identify patterns of soil formation in a particular area, and the other is a segment of direct methods based on technical analysis tools. In particular, a group of direct methods can use special instruments, devices, and appliances that make it possible to determine particle parameters with a high degree of accuracy. In particular, electron and optical microscopes that implement micrometric studies can be used. The direct method allows you to more accurately determine the particle size distribution of the soil, however, due to the difficulties of the technical organization of the process and the high cost it is used extremely rarely.
Indirect methods for determining composition
This group of methods for determining the composition usually includes methods that are based on the application of different laws in the structure of the test mixture. In particular, dependencies between the elements of the array themselves can be detected, but more often complex analysis is supposed. That is, in the process of comparison, other soil characteristics are also taken into account, among which moisture, suspension properties, sedimentation dynamics, etc. Indirect methods for determining the particle size distribution also involve optical and areometric methods for recording physical qualities. In addition, the latest technology allows the use and modeling of natural sedimentation. If we compare this direction of analysis with direct methods, then its disadvantages include low accuracy. Therefore, if it is required to conduct a one-time study on a specific site, then a direct method will still be preferable. But in large-scale and regular work economically only indirect methods justify themselves economically.
Areometric method
This is a highly specialized, albeit popular, technique that is based on the principles of displaced fluid. Actually, this is how the hydrometer used in the analysis process works. The principle itself operates according to the rule according to which the volume of liquid displaced will be equivalent to the mass replaced by a new body. Only in the case of the practice of using the hydrometric technique, the granulometric composition of the soil is determined through the collected suspension. In particular, the specialist also by immersion of particles in water checks the deviations from the data obtained previously. Typically, such an analysis is performed in series, and in each case, work is carried out to determine one characteristic - density. Again, based on the relationship of the particles and the conditions of their stay in the soil, one can thus determine the fractional and mechanical composition.
Pipette method
In this case, a liquid medium is also used, which makes it possible to distinguish individual particles by characteristics. The sample taken is immersed in water, after which the rate of fall of the composition elements is recorded. After a certain period of time, the analysis is completed, and the settled particles are removed. Then the sample is dried, measured and a report is generated based on the results of the audit. As a rule, the determination of particle size distribution by this technique is used in the analysis of clay soils. This is due precisely to the fact that the particles in such soil have a fine fraction, which can be analyzed by the rate of fall in liquid media.
Rutkowski Method
Like all indirect methods of composition analysis, this technique does not differ in high accuracy and gives only a general idea of the elements contained in the studied mass. The very principle of determining the characteristics of particles by the Rutkovsky method is based on two parameters. First of all, this is the same rate of fall of an element in a liquid medium. But in this case, the dependence is not traced between the speed and the origin of the particle, but in relation to the dynamics of immersion to size. And the second parameter, which allows you to determine the particle size distribution of the soil using this technique, is based on the ability of the particles to swell in the same aqueous medium. In this part of the analysis, both physical and, in some way, chemical qualities of the mass are revealed.
Sieve method
This is one of the oldest and most common methods for determining soil composition. It is based on the use of special sets of sieves that pass fractions of the same size, and do not pass particles with larger parameters. The method is simple and affordable to use, so it is often used in the construction industry, where it is not possible to organize complex methods of indirect analysis. However, checking the composition through a sieve cannot be reliably attributed to direct methods. Nevertheless, such an analysis will not make it possible to determine, for example, the granulometric composition of rocks with the same degree of accuracy as a micrometric study will do. True, accuracy will largely depend on the analysis tool - that is, the set of screens. There are two categories of these devices. One of them focuses on sieving without rinsing. In this case, the cells have a size of from 0.5 to 10 mm. Another group is sieves having a passage fraction of 0.1 to 10 mm.
How does particle size distribution affect plants?
Both the fraction and the presentation of different minerals affect the agro-technical properties of the soil. In particular, the composition can determine the air-water environment of the soil, its tendency to erosion processes, aggregation, density, biological and chemical qualities. So, for example, sandy and clay soils cause a weak environment in terms of air and humidity exchange. This is detrimental to most plants - especially those grown on agricultural land, where the nature of the cultivation also affects the fertile layer. But the particle size distribution is important for vegetation not so much in terms of structure and density as in the content of useful elements. Sometimes the presence of magnesium, phosphorus and salts in itself provides an optimal layer of the nutrient base, eliminating the need for additional fertilizers.
Conclusion
An example of technological approaches to soil analysis for particle size distribution shows how the latest measuring devices turn out to be uncompetitive in front of research methods using elementary physical rules and regularities. Of course, it cannot be said that the determination of the particle size distribution of the soil through micrometric analysis loses to indirect methods in qualitative performance indicators. But in terms of practicality, it is the second group that is more effective. Moreover, the very concept of using high-precision technical means is not canceled at all. The most promising methods just involve the combination of two research principles.